Development in ultrasound technology has become an essential tool to medical professionals for more accurate diagnoses of diseases and other health conditions in their patients. Due to the non-invasive nature of the ultrasound, such a tool is considerably safer than other diagnostic instruments, such as X-rays that use high energy electromagnetic radiation. The ultrasound system works as an imaging technique by sending a high-frequency sound wave through internal body parts and receives a return echo. Next, the return echo from the sound wave generates a corresponding image that may then be used for medical examination. Such a system, used as a diagnostic instrument, has proven to be valuable in the practice of medicine. Although extremely high power levels of ultrasounds, such as those used to treat kidney stones, may heat up the body, no known instance of harm or injury has resulted from exposure to the lower energy levels used for diagnostic ultrasound waves, thus indicating an excellent safety record, even after several decades of use [E]. In consideration of the benefits to using ultrasound technology, physicians and other medical professionals are more likely to prefer using ultrasound system as a screening and researching tool rather than any other existing systems, for example x-rays.
With the advent of micro-processor technology and recent developments in computing power, generating three-dimensional (3-D) images from ultrasound waves is now possible. For real three-dimensional (3-D) imaging with two dimension (2-D) transducers (e.g., 50×50 channels), developments have made such technology feasible mainly to academic research. 2-D transducers demand channels in the order of 1000s, for instance, and the number of channels is proportional to the cost, such that the higher the number of channels required, the costlier the equipment; thus using such a system for common monitoring purposes is a bit unrealistic. Furthermore, such a transducer would need to be roughly greater than the size of an ordinary computer mouse, and for a device of that size to be placed on a patient's body for a possibly long duration of time renders such 2-D transducers rather impractical. In short, due to such a 2-D system's complexity and costly equipment, use of it in the commercial environment has been quite limited. While a solution[C] to lift this limitation would be the application of 2-D sparse array (array with removed elements), an application which demand channels in the order of 100s, such systems are still considered too bulky and not cost-effective.
On the other hand, the commercial monitoring systems currently available employs a single or dual element transducer, which requires manual or at least motor-servo operator assistance in monitoring applications. Being highly dependent on a clinical professional's continuous attention on the monitoring application, such a system would be subject to human error. The disadvantages and limitations of the aforementioned systems create a need for a simpler, more compact and cost-effective ultrasound system. 1-D transducers require only channels in the order of 10s (rather than 1000s like 2-D transducers) and may be produced in a more compact size than the other systems. The 1-D system is cost-effective and small enough in size to make it practical to fasten to a patient's body, which makes this system user-friendly and feasible in the hospital and/or clinical environment as a patient monitoring device.
Doppler ultrasound technology serves many invaluable purposes to medical examination applications. Such applications include but are not limited to the detection and assessment of peripheral arterial diseases, and the detection of emboli (blood clots or other obstructions lodged in a blood vessel) that flow through the blood stream during open heart surgery or other cardiac-related operations. However, there are several drawbacks to the current Doppler ultrasound technology in use by most medical professionals. The current commercial Doppler ultrasound system works through an operator-held transducer that needs to be positioned manually. Though there are some devices employed for positioning and securing the transducer (5,105,815) to the body, the maximum Doppler signal can still be easily missed due to movements from either the operator or the patient. Even the mechanical servo (5,844,140), also used to search for the maximum signal, requires human control and therefore proves unreliable for long-term monitoring purposes.
Ultrasound technology, as applied to transcranial Doppler (TCD), also serves as an important and economical tool for physicians in diagnosing the conditions of patients suffering from stroke-related diseases and brain injuries. Likewise, TCD is useful in detecting vasospasms and blockages in blood vessels by measuring ultrasound Doppler shift related to fluctuation in blood flow velocities. Yet TCD examinations are not performed in the clinical and hospital setting as often as they should be due to the application being extremely operator-dependent. TCD examinations demand an exceptionally steady hand, and thus are still rather not practical or effective in general use. Additionally, the application demands continuous monitoring of patients by highly trained and costly professionals, which may in effect cause an increase in administration costs. Altogether, these drawbacks make an otherwise advantageous application of TCD to be, in practice, very inefficient. Consequently, there is a strong demand and need for an ultrasonic system that goes beyond the current TCD technology to provide more accurate, reliable Doppler information and also perform continuous monitoring on a patient during or after surgery.
Another application of ultrasound technology is the calculation of flow-mediated dilation (FMD), or the measure of the ability of an artery to relax in response to increases in blood velocity, which is essential for cardiovascular research and related clinical applications as FMD provides the data central for determining vascular health. FMD[F] data further assists in furnishing imperative insights into the pre-intrusive phase of the disease atherosclerosis and can detect early signs of the same as well.
The FMD calculation is the computation of the change in post-stimulus arterial diameter, which is typically expressed as the percentage of the baseline diameter before the reactive hyperemia. To measure FMD, an ultrasound wave first scans the brachial artery longitudinally. This is done by holding a transducer securely in place with a stereo tactic clamp. The transducer must be held manually in place for the entire duration of the procedure. Then, a clear section of the vessel must be identified and displayed by the ultrasound system. Manually, again, the maximal change in the Doppler signal is ascertained for purposes of calculating the distance between the opposite lumen-arterial interfaces. As the ultrasound scans are performed continuously on the brachial artery, a blood pressure cuff fastened around the patient's forearm distal is inflated repeatedly over a length of time (e.g., five minutes) then abruptly deflated to artificially generate a reactive hyperemia that will cause the brachial artery to dilate. Finally, the mean diameters of the brachial artery as measured before, during, and after the artificially generated reactive hyperemia are used to calculate the percentage increase in FMD. Patients suffering from coronary artery diseases (CAD), cardiovascular diseases, or diabetes mellitus (DM), when monitored by the manually and statically secured FMD system, normally produces lower values of FMD than healthy individuals; therefore, to effectively monitor and regulate their particular conditions, the constant monitoring of their FMD levels is vital.
In light of the importance of accurate techniques for measuring brachial FMD, a better alternative to the traditional manual assessments is greatly needed. Currently, FMD analysis is prone to human error as the manual assessment of the vessel's diameter is done through a visual inspection and manually aligning the transducer. Such manual assessment and alignment is subject to severe observer errors. Also, the measurements can be thrown off by movements from the patient. In calculation, the percentage increase in the measure of FMD is in the order of 10%, thus even a slight change of transducer alignment along the longitudinal direction could result in imprecision. An imprecision in calculation could then easily cause dangerous misinterpretations by the reader. For this reason among others, it is necessary to have a way in which the transducer can be fastened and kept on the patient steadily and continually while Doppler signals are monitored, unencumbered by the reader's or the patient's movements.
U.S. Pat. No. 6,682,483 discloses a device using Doppler ultrasound to monitor blood velocity data with 3-D imaging that can be used for long-term, unattended blood flow monitoring in medical applications. In one embodiment, the invention comprises of a pad and processor that collects the Doppler data in a 3-D region through an array of sonic transducer elements, locking onto and tracking the points in the three-dimensional space to locate maximum blood velocity. This invention is limited by its 3-D imaging process, which would require a larger transducer and thus not be easily attachable to a patient's body. The invention is further limited in that it uses Mono-pulse tracking technique, known in the radar industry to track objects in air using electromagnetic wave as a medium, which is inefficient and impractical in its implementation due to ultrasound's strong frequency-dependent attenuation and nonlinear propagation in the human body, skull and blood vessels. The prior art also does not produce strong enough signals to overcome the noises and attenuation that are associated with ultrasound imaging processes.
On the other hand, the present invention solves the aforementioned issues with current monitoring procedures because it has the capability of transmitting automatically-aligning ultrasound beams into a patient and thus obtains the optimized Doppler signal for remarkably accurate results. The function of said invention will prove indispensable to a cardiac surgeon during and post-operation because it provides immediate information to the surgeon regarding the patient's degree of recovery, potential risk factors for stroke and/or other related health complications. Additionally, blood flow measured by Doppler shifts rather than other forms of measurement is quantified more accurately, which will facilitate a more precise judgment of the patient's condition. For example, some patients run the risk of suffering strokes post-surgery due to embolism, a condition where arteries are blocked by emboli or blood clots that travel up to the brain. Stroke is a leading cause of serious, long-term disability in such patients and is furthermore the third leading cause of death in the United States, behind heart disease and cancer [A]. But the ongoing measurements taken from this invention can provide early detection of emboli and stroke symptom as it analyzes the patient's blood flow condition, which in turn allows the surgeon to take preventive measures before complications even arise and thereby reducing chances of permanent brain damage in such patients and even potentially saving such patients' lives.